The usual word for “horse” in Sindarin, a derivative of ✶rokkō (Let/282, 382) and very well attested. There are indications that this word was more specifically a “swift horse” (Let/382; EtyAC/ROK), but in most cases Tolkien used it generically.
Conceptual Development: The first precursor to this word seems to be G. brog “horse” from the Gnomish Lexicon of the 1910s (GL/24), though at the time it had no Qenya cognates. ᴱN. brog “horse” reappeared in Early Noldorin Word-lists of the 1920s (PE13/139), but by The Etymologies of the 1930s it had become N. roch “horse”, already with the derivation given above (Ety/ROK; EtyAC/ROK). Tolkien seems to have mainly stuck with this form thereafter.
A neologism coined by Paul Strack in 2018 specifically for Eldamo, serving as a replacement for G. idra “dear, valued, precious” (GL/50) and inspired by ON. mirya “precious” (Ety/MIR); compare S. cair < ✶kiryā.